ABSTRACT Although extracellular matrix (ECM) remodeling is a natural response to injury, excessive ECM deposition, or fibrosis, limits regeneration, is a causative factor in hundreds of diseases, and leads to 40% of all deaths worldwide. Fibrosis occurs in salivary glands (SG) of patients treated with radiation for head and neck cancers and in patients suffering from the autoimmune disease, Sjgren?s Syndrome (SS). Despite the known inhibitory effects of fibrosis on tissue regeneration, and involvement of fibrosis in disease, the mechanisms through which fibrosis develops in the salivary gland and leads to dysfunction have not been explored. The stroma of salivary glands and other organs includes tissue-resident mesenchymal stem cells (MSCs). MSCs have inherent anti-fibrotic and anti-inflammatory functions; however, in disease states tissue- resident MSCs can undergo conversion into myofibroblasts (myo-FBs) and contribute to fibrosis. Therapeutic transplantation of MSCs has been used to treat many inflammatory disorders, with the most common tissue source for therapeutic MSCs being bone marrow (BM). Injection of BM-MSCs into non-obese diabetic (NOD) mice, a commonly used mouse model for SS, showed decreased inflammation and some limited SG functional restoration; however, effects were transient and the mechanisms leading to restored function remain unknown. Therapies that manipulate endogenous or apply exogenous MSCs hold clinical promise for diseases involving fibrosis and salivary hypofunction. Mechanisms through which tissue-resident MSCs and transplanted MSCs become fibrosis-generating myo-FBs in the SG are unknown; however, in many tissues signaling by Gli1 is required. We hypothesize that tissue-resident MSCs that undergo conversion to myo-FBs leading to fibrotic connective tissue exacerbating autoimmune disease and salivary dysfunction. The objective of this proposal is to determine if modulation of tissue-resident MSCs can limit fibrosis, inflammation, and restore gland function in injured and diseased salivary glands. We will address several important clinically relevant questions in this proposal: 1) Does Gli1 signaling contribute to fibrosis in injured/diseased salivary glands? 2) Can tissue- resident myo-FBs revert to a pro-regenerative MSC state and what are the associated genetic changes that demark this conversion? 3) In a murine Sjgren?s Syndrome model, will limiting conversion of tissue-resident MSCs into myo-FBs limit fibrosis, decrease disease progression, and facilitate functional restoration? The outcomes of our proposed study are expected to improve scientific knowledge by revealing cellular mechanisms through which MSCs contribute to fibrosis in SG. These findings will have a positive impact by identifying potential therapeutic targets. In addition, we will optimize scaffold delivery systems for MSCs and anti-fibrotic pharmacologicals for reducing fibrosis and restoring function in hypofunctioning salivary glands and other organs.